Optical device

ABSTRACT

There is provided an optical device including a display device, and a transparent substrate that is disposed on a side of a display surface of the display device. When the transparent substrate is evaluated by using a three index values of a resolution index value T, a reflection image diffusiveness index value R, and a sparkle index value S, the following conditions are satisfied: the resolution index value T≤0.2, the reflection image diffusiveness index value R≥0.2, and the sparkle index value S≤60.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application filed under 35U.S.C. 111(a) claiming benefit under 35 U.S.C. 120 and 365(c) of PCTInternational Application No. PCT/JP2014/053218 filed on Feb. 12, 2014and designating the U.S., which claims priority to Japanese PatentApplication No. 2013-030238 filed on Feb. 19, 2013 and Japanese PatentApplication No. 2013-082670 filed on Apr. 11, 2013. The entire contentsof the foregoing applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical device.

2. Description of the Related Art

In general, on a side of a display surface of a display device, such asa liquid crystal display (Liquid Crystal Display: LCD), a cover that isformed of a transparent substrate is disposed so as to protect thedisplay device.

However, when such a transparent substrate is disposed on the displaydevice, and when a displayed image of the display device is attempted tobe viewed through the transparent substrate, often, an object that isdisposed in the vicinity can be reflected. When such a reflection occurson the transparent substrate, it may become difficult for a personviewing the displayed image to view the displayed image, and the personviewing the image may have an unpleasant impression. Especially, forcover glass that is installed inside a vehicle, a strong light sourcethat is represented by sunlight can be reflected. Thus, it can becomevery difficult to view a displayed image, and it is possible thatdriving is adversely affected because necessary information cannot beread.

Thus, for preventing such a reflection from occurring, for example, amethod has been adopted that is for implementing an anti-glare processthat is for forming an uneven shape on the surface of the transparentsubstrate.

Note that Patent Document 1 discloses a method of evaluating areflection on the display device by using a special device.

-   Patent Document 1: Japanese Unexamined Patent Publication No.    2007-147343

As described above, Patent Document 1 shows the method of evaluating thereflection on the display device using the special device.

However, optical characteristics that are required for cover glass thatis installed inside a vehicle is not limited to reduction of reflection.Namely, cover glass that is installed inside a vehicle may be requiredto have predetermined levels of optical characteristics, such as for aresolution, reflection image diffusiveness, and sparkle, respectively.Accordingly, for selecting a transparent substrate, it may beinsufficient to consider only one of the optical characteristics. Often,there may arises a need to consider a plurality of opticalcharacteristics at the same time.

The resolution that is described here is for representing whether and towhat extent an image that matches a displayed image can be obtained whenthe displayed image is viewed through a transparent substrate. Further,the reflection image diffusiveness is for representing to what extent areflected image of an object that (e.g., a light) is disposed in thevicinity of the transparent substrate matches the original object.Furthermore, the sparkle is for representing to what extent unevennessof a bright spot is observed that occurs when light (an image) from thedisplay image passes through the transparent substrate, the light isreflected by the surface of the transparent substrate, and the scatteredlight beams mutually interfere.

Among the optical characteristics that are required for the transparentsubstrate, there are often characteristics that are in tradeoffrelationships. For example, in general, in order to enhance thereflection image diffusiveness, the anti-glare process is applied to thesurface of the transparent substrate. However, when such an anti-glareprocess is applied, a resolution of the transparent substrate tends tobe lowered. In this manner, when the anti-glare process is to be appliedto the transparent substrate based on a plurality of opticalcharacteristics, it may become difficult to select a proper anti-glareprocess.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of such a background. Anobject of the present invention is to provide an optical device having aresolution, reflection image diffusiveness, and an anti-glare propertythat are suitable for automotive use.

According to the present invention, there is provided an optical deviceincluding a display device and a transparent substrate that is disposedon a side of a display surface of the display device, wherein thetransparent substrate has a first surface and a second surface, andwherein, when the transparent substrate is evaluated by using a threeindex values of a resolution index value T, a reflection imagediffusiveness index value R, and a sparkle index value S that arequantified by following methods,

the resolution index value T≤0.2,

the reflection image diffusiveness index value R≥0.2, and

the sparkle index value S≤60

are satisfied.

Here, for the resolution index value T, a first light beam is irradiatedfrom a side of the second surface of the transparent substrate in adirection that is parallel to a thickness direction of the transparentsubstrate (a direction of an angle of 0°), and brightness of atransmitted light beam that is transmitted from the first surface (whichis referred to as 0° transmitted light beam) is measured, a lightreception angle of receiving the first light beam with respect to thefirst surface of the transparent substrate is varied in a range from−90° to +90°, brightness of all the transmitted beams that aretransmitted from a side of the first surface is measured, and theresolution index value T is calculated from following expression (1):the resolution index value T=(the brightness of all the transmittedbeams−the brightness of the 0° transmitted light beam)/(the brightnessof all the transmitted light beams)  expression (1).

For the reflection image diffusiveness index value R, a second lightbeam is irradiated from the side of the first surface of the transparentsubstrate in a direction of 45° with respect to the thickness of thetransparent substrate, brightness of a light beam that is specularlyreflected by the first surface (which is referred to as a 45° regularreflected light beam) is measured, a light reception angle of receivingthe reflected beam that is reflected by the first surface is varied in arange from 0° to +90°, brightness of all the reflected beams that arereflected by the first surface is measured, and the reflection imagediffusiveness index value R is calculated by following expression (2):the reflection image diffusiveness index value R=(the brightness of allthe reflected beams−the brightness of the 45° regular reflectedbeam)/(the brightness of all the reflected beams)  expression (2).

For the sparkle index value S, the transparent substrate is arranged atthe side of the display surface of the display device so that the secondsurface is at the side of the display device, a photograph of thetransparent substrate is taken from the side of the first surface toobtain an image, the image is analyzed by software EyeScale-4W (aproduct of I-System Co., Ltd.), and the sparkle index value S isobtained by setting an ISC-A value that is output by the software as thesparkle index value S.

Here, in the optical device according to the present invention, thedisplay device may be one device that is selected from a group thatincludes a liquid crystal display (LCD) device, an organiclight-emitting diode (OLED) device, and a plasma display panel (PDP)device.

Further, in the optical device according to the present invention, thetransparent substrate may be formed of soda-lime glass oraluminosilicate glass.

Further, in the optical device according to the present invention, achemically strengthening process may be applied to at least one of thefirst surface and the second surface of the transparent substrate.

Further, in the optical device according to the present invention, ananti-glare process may be applied to the first surface.

Further, the optical device according to the present invention may be anoptical device that is to be installed inside a vehicle.

According to the present invention, there can be provided an opticaldevice that has a resolution, reflection image diffusiveness, and ananti-glare property that are suitable for installation inside a vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a flow of a method ofobtaining a resolution index value of a transparent substrate accordingto an embodiment of the present invention;

FIG. 2 is a diagram schematically showing an example of a measurementdevice that is used for obtaining the resolution index value;

FIG. 3 is a diagram schematically showing a flow of a method ofobtaining a reflection image diffusiveness index value of thetransparent substrate according to the embodiment of the presentinvention;

FIG. 4 is a diagram schematically showing an example of a measurementdevice that is used for obtaining the reflection image diffusivenessindex value;

FIG. 5 is a diagram schematically showing a flow of a method ofobtaining a sparkle index value of the transparent substrate accordingto the embodiment of the present invention;

FIG. 6 is a diagram that is obtained by plotting an example of arelationship between the resolution index value T (a horizontal axis)and the reflection image diffusiveness index value R (a vertical axis)that is obtained for each type of the transparent substrate;

FIG. 7 is a diagram that is obtained by plotting an example of arelationship between the sparkle index value S (a horizontal axis) andthe reflection image diffusiveness index value R (a vertical axis) thatis obtained for each type of the transparent substrate;

FIG. 8 is a diagram that is obtained by plotting an example of arelationship between the resolution index value T (a horizontal axis)and the sparkle index value S (a vertical axis) that is obtained foreach type of the transparent substrate;

FIG. 9 is a schematic three-dimensional diagram in which the resolutionindex value T, the reflection image diffusiveness index value R, and thesparkle index value S are set as axes, respectively;

FIG. 10 is a cross-sectional view schematically showing an opticaldevice according to an embodiment;

FIG. 11 is a graph showing an example of a relationship between adetermination result of a resolution level by a visual observation (avertical axis) and the resolution index value T (a horizontal axis) thatis obtained for each type of the transparent substrate;

FIG. 12 is a diagram that collectively shows transparent substrates thathave the reflection image diffusiveness index values from level 1 tolevel 12, respectively;

FIG. 13 is a graph showing an example of a relationship between a levelof the reflection image diffusiveness index value by a visualobservation (a vertical axis) and the reflection image diffusivenessindex value R (a horizontal axis) that is obtained for each type of thetransparent substrate;

FIG. 14 is a diagram showing transparent substrates that indicatesparkle of level 0 and sparkle of level 7, respectively; and

FIG. 15 is a graph showing an example of a relationship between thesparkle index value S (a vertical axis) and the level of the sparkle bya visual observation (a horizontal axis) that is obtained for eachtransparent substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is explained in detail below.

According to the present invention, there is provided an optical deviceincluding a display device and a transparent substrate that is disposedat a side of a display surface of the display device, wherein thetransparent substrate has a first surface and a second surface, andwherein, when the transparent substrate is evaluated by using threeindex values of a resolution index value T, a reflection imagediffusiveness index value R, and a sparkle index value S that arequantified by the following method,

the resolution index value T≤0.2,

the reflection image diffusiveness index value R≥0.2, and

the sparkle index value S≤60

are satisfied.

Here, for the resolution index value T, a first light beam is irradiatedfrom a side of the second surface of the transparent substrate in adirection that is parallel to a thickness direction of the transparentsubstrate (a direction of an angle of 0°), and brightness of atransmitted light beam that is transmitted from the first surface (whichis referred to as 0° transmitted light beam) is measured, a lightreception angle of the first light beam with respect to the firstsurface of the transparent substrate is varied in a range from −90° to+90°, and brightness of all the transmitted beams that are transmittedfrom a side of the first surface is measured, and the resolution indexvalue T is calculated from following expression (1):the resolution index value T=(the brightness of all the transmittedbeams−the brightness of the 0° transmitted light beam)/(the brightnessof all the transmitted light beams)  expression (1).

For the reflection image diffusiveness index value R, a second lightbeam is irradiated from the side of the first surface of the transparentsubstrate in a direction of 45° with respect to the thickness of thetransparent substrate, brightness of a light beam that is specularlyreflected by the first surface (which is referred to as a 45° regularreflected light beam) is measured, a light reception angle of receivingthe reflected beam that is reflected by the first surface is varied in arange from 0° to +90°, brightness of all the reflected beams that arereflected by the first surface is measured, and the reflection imagediffusiveness index value R is calculated by following expression (2):the reflection image diffusiveness index value R=(the brightness of allthe reflected beams−the brightness of the 45° regular reflectedbeam)/(the brightness of all the reflected beams)  expression (2).

For the sparkle index value S, the transparent substrate is arranged atthe side of the display surface of the display device so that the secondsurface is at the side of the display device, a photograph of thetransparent substrate is taken from the side of the first substrate toobtain an image, the image is analyzed by software EyeScale-4W (aproduct of I-System Co., Ltd.), and the sparkle index value S isobtained by setting an ISC-A value that is output in this manner as thesparkle index value S.

As described above, for a transparent substrate that is disposed on aside of a surface of a display device, various optical characteristicsare required, such as a resolution, reflection image diffusiveness, andan anti-glare property. Thus, for selecting a transparent substrate,there are often cases where it is insufficient to consider only a singleoptical property.

In contrast, according to the present invention, three opticalcharacteristics of the transparent substrate that are a resolution indexvalue, a reflection image diffusiveness index value, and a sparkle indexvalue are objects of the determination.

In such a method, a transparent substrate can be more properly selectedbecause the transparent substrate can be selected by comprehensivelyconsidering three optical characteristics.

Further, in the method according to the present invention, values thatare expressed in numerical forms are used as the resolution index value,the reflection image diffusiveness index value, and the sparkle indexvalue of the transparent substrate. Consequently, the opticalcharacteristics of the resolution, the reflection image diffusiveness,and the sparkle can be objectively and quantitatively determined withoutdepending on a subjective view and prejudice of an observer.

Further, among the optical characteristics that are required for thetransparent substrate, there are often optical characteristics that arein tradeoff relationships, such as the resolution and the reflectionimage diffusiveness. According to related art, in such a case, sincethere is no index that can be a basis for the selection, it has beendifficult to properly select a transparent substrate with which twooptical characteristics are satisfied. Furthermore, when three opticalcharacteristics are to be considered, it has been almost impossible toselect a transparent substrate that satisfies these opticalcharacteristics.

In contrast, in the method according to the present invention, threeoptical characteristics of a transparent substrate can be quantitativelyand comprehensively evaluated. Thus, in the method according to thepresent invention, a transparent substrate that has the optimum opticalcharacteristics can be properly selected depending on purpose and use.

Hereinafter, an embodiment of a method of obtaining a resolution indexvalue, a reflection image diffusiveness index value, and a sparkle indexvalue of a transparent substrate, which can be used in the methodaccording to the present invention, is explained by referring to thedrawings.

(Regarding the Resolution Index Value)

FIG. 1 schematically shows a flow of a method of obtaining a resolutionindex value of a transparent substrate according to an embodiment of thepresent invention.

As shown in FIG. 1, the method of obtaining the resolution index valueof the transparent substrate includes

(a) a step of irradiating a first light beam from a side of a secondsurface of the transparent substrate having a first surface and thesecond surface in a direction that is parallel to a thickness directionof the transparent substrate, and measuring brightness of a transmittedbeam (which is also referred to as “0° transmitted light beam,”hereinafter) that is transmitted in a direction that is parallel to thethickness direction of the transparent substrate from the first surface(step S110),

(b) a step of varying a light reception angle for receiving the firstlight beam with respect to a thickness direction of the transparentsubstrate in a range from −90° to +90°, and measuring brightness of thefirst light beam (which is also referred to as “all the transmittedbeams,” hereinafter) that passes through the transparent substrate andthat is emitted from the first surface (step S120), and

(c) a step of calculating a resolution index value T by the followingexpression (1) (step S130):the resolution index value T=(the brightness of all the transmittedbeams−the brightness of the 0° transmitted light beam)/(the brightnessof all the transmitted beams)  expression (1).

Hereinafter, each of the steps is explained.

(Step S110)

First, a transparent substrate is prepared that has a first surface anda second surface that face each other.

The transparent substrate may be formed of any material, provided thatit is transparent. The transparent substrate may be glass or plastic,for example.

When the transparent substrate is formed of glass, composition of theglass is not particularly limited. For example, the glass may besoda-lime glass or aluminosilicate glass.

Further, when the transparent substrate is formed of glass, a chemicallystrengthening process may be applied to the first surface and/or thesecond surface.

Here, the chemically strengthening process is said to be a general termof a technique for replacing an alkali metal (ions) having a small ionicradius that exists on an outermost surface of the glass substrate withan alkali metal (ions) having a large ionic radius that exists in adissolved salt by immersing a glass substrate in the dissolved salt thatincludes the alkali metals. In the chemically strengthening process, analkali metal (ions) having an ionic radius that is greater than that ofthe original atom is disposed on the surface of the processed glasssubstrate. Thus, compressive stress can be provided on the surface ofthe glass substrate, thereby enhancing the strength of the glasssubstrate (especially, break strength).

For example, when the glass substrate includes a sodium ion (Na+), thissodium ion is replaced with a potassium ion (Ka+) by the chemicallystrengthening process. Alternatively, for example, when the glasssubstrate includes a lithium ion (Li+), this lithium ion may be replacedwith a sodium ion (Na+) and/or a potassium ion (Ka+) by the chemicallystrengthening process.

When the transparent substrate is formed of plastic, composition of theplastic is not particularly limited. For example, the transparentsubstrate may be a polycarbonate substrate.

Note that, prior to step S110, a step of applying an anti-glare processto the first surface of the transparent substrate may be implemented.The method of the anti-glare process is not particularly limited. Forexample, the anti-glare process may be a frost process, an etchingprocess, a sandblast process, a lapping process, or a silica-coatingprocess.

After the application of the anti-glare process, the first surface ofthe transparent substrate may have a surface roughness (an arithmeticaverage roughness Ra) in a range from 0.05 μm to 0.5 μm, for example.

Next, a first light beam is irradiated from a side of the second surfaceof the transparent substrate in a direction that is parallel to athickness direction of the transparent substrate, specifically, in adirection of an angle θ=0°±0.5° (which is also referred to as a“direction of the angle 0°”, hereinafter). The first light beam passesthrough the transparent substrate, and the first light beam isirradiated from the first surface. The 0° transmitted light beam that isirradiated in the direction of the angle 0° from the first surface isreceived, and its brightness is measured. It is referred to as the“brightness of the 0° transmitted light beam.”

(Step S120)

Next, an angle θ of receiving the light beam that is irradiated from thefirst surface is varied in a range from −90° to +90°, and a similaroperation is executed. In this manner, a brightness distribution of thelight beam that passes through the transparent substrate and that isirradiated from the first surface is measured and summed, therebydefining the “brightness of all the transmitted light beams.”

(Step S130)

Next, the resolution index value T is calculated from the followingexpression (1):the resolution index value T=(the brightness of all the transmittedlight beams−the brightness of the 0° transmitted light beam)/(thebrightness of all the transmitted light beams)   expression (1).

As described below, it has been verified that the resolution index valueT correlates with a determination result of the resolution by visualobservation of an observer, and that it behaves like a human visualsense. For example, for a transparent substrate whose resolution indexvalue T indicates a large value (close to 1), the resolution isunfavorable, and conversely, for a transparent substrate whoseresolution index value T indicates a small value, the resolution isfavorable. Accordingly, this resolution index value T can be used as aquantitative index for determining a resolution of a transparentsubstrate.

FIG. 2 schematically shows an example of a measurement device that isused for obtaining the resolution index value T that is represented bythe above-described expression (1).

As shown in FIG. 2, the measurement device 200 includes a light source250; and a detector 270. A transparent substrate 210 is disposed in themeasurement device 200. The transparent substrate 210 has a firstsurface 212 and a second surface 214. The light source 250 emits a firstlight beam 262 toward the transparent substrate 210. The detector 270receives a transmitted light beam 264 that is emitted from the firstsurface 212, and detects its brightness.

Note that the transparent substrate 210 is arranged such that the secondsurface 214 is at the side of the light source 250, and the firstsurface 212 is at the side of the detector 270. Thus, the first lightbeam that is to be detected by the detector 270 is the transmitted lightbeam 264 that passes through the transparent substrate 210. Note that,when an anti-glare process is applied to one of the surfaces of thetransparent substrate 210, the surface to which the anti-glare processis applied is the first surface 212 of the transparent substrate 210.Namely, in this case, the transparent substrate 210 is arranged in themeasurement device 200, so that the surface to which the anti-glareprocess is applied is at the side of the detector 270.

Further, the first light beam 262 is irradiated at an angle θ that isparallel to the thickness direction of the transparent substrate 210.Hereinafter, this angle θ is defined to be 0°. Note that, in thisapplication, by considering an error of the measurement device, therange of θ=0°±0.5° is defined to be the angle 0°.

In such a measurement device 200, the first light beam 262 is irradiatedfrom the light source 250 toward the transparent substrate 210, and thetransmitted light beam 264 that is irradiated from the side of the firstsurface 212 of the transparent substrate 210 is detected by using thedetector 270. In this manner, the 0° transmitted light beam is detected.

Next, the angle θ at which the detector 270 receives the transmittedlight beam 264 is varied in a range from −90° to +90°, and the similaroperation is executed.

In this manner, by using the detector 270, the transmitted light beam264 that passes through the transparent substrate 210 and that isirradiated from the first surface 212 is detected in the range from −90°to +90°, namely, “all the transmitted light beams” are detected.

From the obtained brightness of the 0° transmitted light beam and theobtained brightness of all the transmitted light beams, the resolutionindex value T of the transparent substrate 210 can be obtained by theabove-described expression (1).

Note that such a measurement can be easily implemented by using acommercially available goniometer (a goniophotometer).

(Regarding the Reflection Image Diffusiveness Index Value)

FIG. 3 schematically shows a flow of a method of obtaining a reflectionimage diffusiveness index value of a transparent substrate, according toan embodiment of the present invention.

As shown in FIG. 3, the method of obtaining a reflection imagediffusiveness index value of a transparent substrate includes

(a′) a step of irradiating a second light beam from a side of a firstsurface of the transparent substrate having the first surface and asecond surface in a 45° direction with respect to a thickness directionof the transparent substrate, and measuring brightness of the light beamthat is specularly reflected by the first surface (which is alsoreferred to as the “45° specular reflected light beam,” hereinafter)(step S210),

(b′) a step of varying a light reception angle for receiving the lightbeam that is reflected by the first surface in a range from 0° to +90°,measuring brightness distribution of the second light beam that isreflected by the first surface (which is also referred to as “all thereflected light beams,” hereinafter) (step S220), and measuring thebrightness of the 45° specular reflected light beam (step S210), and

(c′) a step of calculating the reflection image diffusiveness indexvalue R by the following expression (2) (step S230):the reflection image diffusiveness index value R=(the brightness of allthe reflected light beams−the brightness of the 45° specular reflectedlight beam)/(the brightness of all the reflected light beams)  expression (2).

Hereinafter, each of the steps is explained.

(Step S210)

First, a transparent substrate is prepared that has a first surface anda second surface that face each other.

Since a material and composition of the transparent substrate are thesame as those of step S110 that are described above, they are notexplained here.

Next, the second light beam is irradiated from the side of the firstsurface of the prepared transparent substrate in a direction of 45°±0.5°with respect to the thickness direction of the transparent substrate.The second light beam is specularly reflected by the first surface ofthe transparent substrate. Among the reflected light beams, the 45°specular reflected light beam is received, its brightness is measured,and thereby the “brightness of the 45° specular reflected light beam” isdefined.

(Step S220)

Next, the light reception angle of the reflected light beam that isreflected by the first surface is varied in a range from 0° to +90°, andthe same operation is executed. At this time, a brightness distributionof the brightness of the second light beam that is reflected by thefirst surface of the transparent substrate and that is irradiated fromthe first surface is measured and summed, and thereby the “brightness ofall the reflected light beams” is defined.

(Step S230)

Next, the reflection image diffusiveness index value R is calculated bythe following formula (2):the reflection image diffusiveness index value R=(the brightness of allthe reflected light beams−the brightness of 45° specular reflected lightbeam)/(the brightness of all the reflected light beams)   expression(2).

As described below, it has been verified that the reflection imagediffusiveness index value R correlates with a determination result ofthe reflection image diffusiveness by visual observation of an observer,and that it behaves like a human visual sense. For example, for atransparent substrate whose reflection image diffusiveness index value Rindicates a large value (close to 1), the reflection image diffusivenessis favorable, and conversely, for a transparent substrate whosereflection image diffusiveness index value R indicates a small value,the reflection image diffusiveness is unfavorable. Accordingly, thisreflection image diffusiveness index value R can be used as aquantitative index for determining reflection image diffusiveness of atransparent substrate.

FIG. 4 schematically shows an example of a measurement device that isused for obtaining the reflection image diffusiveness index value R thatis represented by the above-described expression (2).

As shown in FIG. 4, the measurement device 300 includes a light source350 and a detector 370. The transparent substrate 210 is disposed in themeasurement device 300. The transparent substrate 210 has the firstsurface 212 and the second surface 214. The light source 350 emits asecond light beam 362 toward the transparent substrate 210. The detector370 receives a reflected light beam 364 that is reflected by the firstsurface 212, and measures its brightness.

Note that the transparent substrate 210 is arranged such that the firstsurface 212 is at the side of the light source 350 and the detector 370.Thus, the second light beam that is detected by the detector 370 is thereflected light beam 364 that is reflected by the transparent substrate210. Further, when an anti-glare process is applied to one of thesurfaces of the transparent substrate 210, the surface to which theanti-glare process is applied is the first surface 212 of thetransparent substrate 210. Namely, in this case, the transparentsubstrate 210 is arranged in the measurement device 300, so that thesurface to which the anti-glare process is applied is at the side of thelight source 350 and the detector 370.

Further, the second light beam 362 is irradiated at an angle φ that istilted by 45° with respect to the thickness direction of the transparentsubstrate 210. Note that, in the present application, by considering anerror of the measurement device, a range of 45°±0.5° is defined to bethe angle of 45°.

In such a measurement device 300, the second light beam 362 is emittedfrom the light source 350 toward the transparent substrate 210, and thereflected light beam 364 that is reflected by the first surface 212 ofthe transparent substrate 210 is detected by using the detector 370. Inthis manner, the “45° specular reflected light beam” is detected.

Next, an angle φ at which the detector 370 measures the reflected lightbeam 364 is varied in a range from 0° to +90°, and the same operation isexecuted.

At this time, the reflected light beam 364 that is reflected by thefirst surface 212 of the transparent substrate 210 in the range from 0°to +90°, namely, a brightness distribution of all the reflected lightbeams is detected and summed by using the detector 370.

From the obtained brightness of the 45° specular reflected light beamand the obtained brightness of all the reflected light beams, thereflection image diffusiveness index value R of the transparentsubstrate 210 can be obtained by the above-described expression (2).

Note that such a measurement can be easily implemented by using acommercially available goniometer (a goniophotometer).

(Regarding the Sparkle Index Value)

FIG. 5 schematically shows a flow of a method of obtaining a sparkleindex value of a transparent substrate, according to an embodiment ofthe present invention.

As shown in FIG. 5, the method of obtaining a sparkle index value of atransparent substrate includes

(a″) a step of disposing a transparent substrate having a first surfaceand a second surface at a side of a display surface of a display deviceso that the second surface of the transparent substrate is at a side ofthe display device (step S310),

(b″) a step of taking a photograph of the transparent substrate from theside of the first surface, and obtaining an image (step S320), and

(c″) a step of quantifying the sparkle of the transparent substrate byanalyzing the image by software EyeScale-4W (a product of I-System Co.,Ltd.) and by using an ISC-A value that is output by the software (stepS330).

Hereinafter, each of the steps is explained in detail.

(Step 310)

First, a transparent substrate is prepared that has a first surface anda second surface that face each other.

Since a material and composition of the transparent substrate are thesame as those of step S110 that are described above, they are notexplained here.

Next, a display device is prepared. The display device is notparticularly limited. For example, the display device may be a liquidcrystal display (LCD) device, an organic light emitting diode (OLED)device, or a plasma display panel (PDP) device. At a side of a displaysurface of the display device, a cover may be provided that is for apurpose of preventing damage or the like.

Next, the transparent substrate is disposed on the side of the displaysurface of the display device. At this time, the transparent substrateis disposed on the display surface of the display device, so that thesecond surface is at the side of the display device.

(Step S320)

Next, a photograph of the transparent substrate is taken from the sideof the first surface in a state in which the display device is turned on(i.e., a state in which an image is displayed), and an image of thetransparent substrate that is disposed on the display device isobtained.

The image that is displayed on the display device may preferably be animage in a single color (e.g., green), and may preferably be displayedon the whole display screen of the display device. That is forminimizing an effect, such as a difference in appearance due to adifference in the displayed color.

For taking the photograph, a digital camera having, at least, a largepixel number (number of pixels) may preferably be used. It maypreferably have an area of an image sensor and a number of pixels thatare sufficient for determining, at least, a size that is smaller thanthe surface unevenness of the transparent substrate after applying theanti-glare process and that is smaller than a pixel pitch.

An image of the transparent substrate that is captured is input into ananalysis device (e.g., a computer).

(Step S330)

Next, an image of the transparent substrate that is captured is analyzedby analysis software. As the analysis software, the EyeScale-4W (aproduct of I-System Co. Ltd.) is used. As a result of the analysis, anISC-A value is output, and this is defined to be a sparkle index valueS.

As described below, it has been verified that the sparkle index value Scorrelates with a determination result of the sparkle by visualobservation of an observer, and that it behaves like a human visualsense. For example, for a transparent substrate whose sparkle indexvalue S is a large value, the sparkle tends to be significant, andconversely, for a transparent substrate whose sparkle index value S is asmall value, the sparkle tends to be suppressed. Accordingly, thissparkle index value S can be used as a quantitative index fordetermining sparkle of a transparent substrate.

By using the above-described resolution index value T, the reflectionimage diffusiveness index value R, and the sparkle index value S,optical characteristics of a transparent substrate can be quantitativelyevaluated.

(Evaluation by Three Indexes)

Next, there is explained a method of comprehensively evaluating threeoptical characteristics of a transparent substrate and its effect.

(A Case of Evaluation by Two Indexes)

First, as a preliminary explanation, a case is explained in whichoptical characteristics of a transparent substrate are evaluated byusing two indexes.

First, for a case of simultaneously evaluating a resolution andreflection image diffusiveness of the transparent substrate, acorrelation diagram, such as shown in FIG. 6, is used.

FIG. 6 is a diagram that is obtained by plotting an example of arelationship between the resolution index value T (the horizontal axis)and the reflection image diffusiveness index value R (the vertical axis)that are obtained for various types of transparent substrates. In thefigure, as the resolution index value T of the horizontal axis becomessmaller, the resolution of the transparent substrate is enhanced, and asthe reflection image diffusiveness index value R of the vertical axisbecomes greater, the reflection image diffusiveness of the transparentsubstrate is enhanced.

Note that, in FIG. 6, for reference, an ideal area of the transparentsubstrate that has both a favorable (high) resolution and favorablereflection image diffusiveness is indicated by a circle mark that isindicated as “Ideal.”

Here, as before, when a candidate transparent substrate is to beselected among various types of transparent substrates by onlyconsidering a single optical characteristic, for example, by onlyconsidering the resolution, transparent substrates that are included inthe area A that is indicated in FIG. 6 by the hatching are to beuniformly selected. Namely, with such a method, a transparent substratewhose reflection image diffusiveness is unfavorable may be included inthe transparent substrates that are the candidates of the selection.Similarly, when a transparent substrate is to be selected by consideringonly the reflection image diffusiveness, transparent substrates that areincluded in the area B that is indicated in FIG. 6 by the hatching areto be uniformly selected, and a transparent substrate whose resolutionis unfavorable may be included in the transparent substrates that arethe candidates of the selection.

Further, as described above, the resolution and the reflection imagediffusiveness are in a tradeoff relationship. Thus, it is substantiallyimpossible to obtain a transparent substrate having both thecharacteristics, namely, to obtain a transparent substrate that existsin the area that is indicated by the circle mark. Consequently, a propertransparent substrate may not be selected only by separately consideringthe resolution and the reflection image diffusiveness.

In contrast, when the correlation diagram of the resolution index valueT and the reflection image diffusiveness index value R, such as shown inFIG. 6, is used, a proper transparent substrate can be selected bysimultaneously considering both the optical characteristics. Namely, insuch a selection method, a transparent substrate can be properlyselected, depending on purpose and use. Namely, with respect to theresolution and the reflection image diffusiveness, a transparentsubstrate can be selected, so that the most favorable characteristicscan be achieved.

Next, FIG. 7 shows a diagram that is obtained by plotting an example ofa relationship between the sparkle index value S (the horizontal axis)and the reflection image diffusiveness index value R (the vertical axis)that is obtained for various types of transparent substrates. In thefigure, as the sparkle index value of the horizontal axis becomessmaller, the sparkle of the transparent substrate is suppressed, and asthe reflection image diffusiveness index value R of the vertical axisbecomes greater, the reflection image diffusiveness of the transparentsubstrate is enhanced.

Note that, in FIG. 7, for reference, an ideal area of the transparentsubstrate that has both a favorable anti-glare property and favorablereflection image diffusiveness is indicated by a circle mark that isindicated as “Ideal.”

For the case of the anti-glare property and the reflection imagediffusiveness, when a candidate transparent substrate is to be selectedamong various types of transparent substrates by considering a singleoptical property, for example, by only considering the anti-glareproperty, as before, the transparent substrates that are included in thearea C that is indicated in FIG. 7 by the hatching are to be uniformlyselected. Namely, with such a method, a transparent substrate havingunfavorable reflection image diffusiveness is to be included in thetransparent substrates that are the candidates of the selection.Similarly, when a transparent substrate is to be selected by onlyconsidering the reflection image diffusiveness, the transparentsubstrates that are included in the area D that is indicated in FIG. 7by the hatching are to be uniformly selected, and a transparentsubstrate having an unfavorable anti-glare property is to be included inthe transparent substrates that are the candidates of the selection.

Further, for the anti-glare property and the reflection imagediffusiveness, it is difficult to optimize both the characteristics, andit is substantially impossible to obtain a transparent substrate suchthat both the characteristics exist in the ideal area that is indicatedby the circle mark. Consequently, a proper transparent substrate may notbe selected only by separately considering the anti-glare property andthe reflection image diffusiveness.

In contrast, when the correlation diagram of the sparkle index value Sand the reflection image diffusiveness index value R, such as shown inFIG. 7, is used, a proper transparent substrate can be selected bysimultaneously considering both the optical characteristics. Namely, insuch a selection method, a transparent substrate can be properlyselected, depending on purpose and use. Namely, with respect to theanti-glare property and the reflection image diffusiveness, atransparent substrate can be selected, so that the most favorablecharacteristics are achieved.

Next, FIG. 8 shows a diagram that is obtained by plotting an example ofa relationship between the resolution index value T (the horizontalaxis) and the sparkle index value S (the vertical axis) that is obtainedfor various types of transparent substrates. In FIG. 8, as theresolution index value T of the horizontal axis becomes smaller, theresolution of the transparent substrate is enhanced, and as the sparkleindex value S of the vertical axis becomes smaller, the sparkle of thetransparent substrate is suppressed (i.e., the anti-glare property isenhanced).

Note that, in FIG. 8, for reference, an ideal area of the transparentsubstrate that has both a favorable resolution and a favorableanti-glare property is indicated by a circle mark that is indicated as“Ideal.”

For the case of the resolution and the anti-glare property, when acandidate transparent substrate is to be selected among various types oftransparent substrates by considering a single optical property, forexample, by only considering the resolution, as before, the transparentsubstrates that are included in the area E that is indicated in FIG. 8by the hatching are to be uniformly selected. Namely, with such amethod, a transparent substrate having an unfavorable anti-glareproperty is to be included in the transparent substrates that are thecandidates of the selection. Similarly, when a transparent substrate isto be selected by only considering the anti-glare property, thetransparent substrates that are included in the area F that is indicatedin FIG. 8 by the hatching are to be uniformly selected, and atransparent substrate having an unfavorable resolution is to be includedin the transparent substrates that are the candidates of the selection.

In contrast, when the correlation diagram of the resolution index valueT and the sparkle index value S, such as shown in FIG. 8, is used, aproper transparent substrate can be selected by simultaneouslyconsidering both the optical characteristics. Namely, in such aselection method, a transparent substrate can be properly selected,depending on purpose and use. Namely, with respect to the resolution andthe anti-glare property, a transparent substrate can be selected, sothat the most favorable characteristics can be achieved.

(A Case of Evaluation by Three Indexes)

Next, a case is explained in which optical characteristics of atransparent substrate are evaluated by using three indexes that are aresolution index value T, a reflection image diffusiveness index valueR, and a sparkle index value S.

In this case, it suffices, further, to add an axis of a third indexvalue to a correlation diagram that is for two evaluation index values,such as shown in FIGS. 6 to 8, that are used in the above-describedsection (the case of evaluation by two indexes). Namely, opticalcharacteristics of a transparent substrate are to be evaluated in athree-axis space that is spanned by a resolution index value T (e.g., anX-axis), a reflection image diffusiveness index value R (e.g., aY-axis), and a sparkle index value S (e.g., a Z-axis).

For example, by adding the sparkle index value S as the Z-axis to thetwo-dimensional diagram of the resolution index value T and thereflection image diffusiveness index value R that is shown in FIG. 6,the three optical characteristics can be represented at the same time.

FIG. 9 is a schematic diagram showing a three-dimensional diagram suchthat its axes correspond to such three optical characteristics. In thefigure, the X-axis is the resolution index value T, the Y-axis is thereflection image diffusiveness index value R, and the Z-axis is thesparkle index value S.

Note that, in FIG. 9, for reference, a region of an ideal transparentsubstrate that has a favorable (high) resolution, favorable reflectionimage diffusiveness, and a favorable anti-glare property is indicated asa region that is surrounded by dotted lines.

However, as described above, the relationship between the resolution andthe reflection image diffusiveness and the relationship between theanti-glare property and the reflection image diffusiveness are tradeoffrelationships. Unfortunately, it is substantially impossible to obtain atransparent substrate that has all the characteristics, namely, atransparent substrate that is included in the region that is surroundedby the dotted lines.

However, when a three-dimensional diagram, such as shown in FIG. 9, isused, a proper transparent substrate can be selected by comprehensivelyconsidering the three optical characteristics, depending on purpose anduse.

For example, for a transparent substrate that is applied to an opticaldevice that is to be installed inside a vehicle, such as a carnavigation system, a high resolution and a high anti-glare property areconsidered to be particularly important factors. Thus, for such a case,it suffices if a transparent substrate having reflection imagediffusiveness that is as favorable as possible (e.g., R≥0.2) isselected, among transparent substrates having small resolution indexvalues T (e.g., T≤0.2) and small sparkle index values S (e.g., S≤60).The portion of FIG. 9 that is indicated by the hatching shows a regionof the candidates for the transparent substrate that is suitable for theoptical device that is to be installed inside a vehicle.

In this manner, in the method according to the embodiment of the presentinvention, the three optical characteristics can be comprehensively andquantitatively considered. Thus, a transparent substrate can be moreproperly selected, depending on purpose and use.

Further, in the method according to the present invention, values thatare expressed in numerical forms are used as the resolution index value,the reflection image diffusiveness index value, and the sparkle indexvalue. Consequently, the optical characteristics of the resolution, thereflection image diffusiveness, and the sparkle can be objectively andquantitatively determined without depending on a subjective view andprejudice of an observer.

(Regarding an Optical Device According to an Embodiment of the PresentInvention)

Next, there is explained an example of a configuration of an opticaldevice according to an embodiment of the present invention by referringto FIG. 10.

FIG. 10 schematically shows a cross section of the optical deviceaccording to the embodiment of the present invention.

As shown in FIG. 10, the optical device 500 includes a display device510 and a transparent substrate 560. The optical device 500 is a displaydevice with cover glass.

The transparent substrate 560 has a first surface 562 and a secondsurface 564. The transparent substrate 560 is disposed on a side of adisplay surface of the display device 510 so that the second surface 564is at the side of the display device 510.

Note that, in the example of FIG. 10, the transparent substrate 560 isdirectly disposed on the side of the display surface of the displaydevice 510. However, the transparent substrate 560 may not be in contactwith the display device 510. Another transparent substrate, or a spacemay be disposed between them.

The transparent substrate 560 may be formed of glass (e.g., soda-limeglass or aluminosilicate glass) or plastic (e.g., polycarbonate), forexample. Further, when the transparent substrate 560 is formed of glass,a chemically strengthening process may be applied to at least one of thefirst surface 562 and the second surface 564 of the transparentsubstrate 560. By doing this, the strength of the transparent substrate560 can be enhanced.

Further, an anti-glare process may be applied to the first surface 562of the transparent substrate 560.

The display device 510 includes a display surface (not shown). Thetransparent substrate 560 is disposed on the display device 510 so as tocover the display surface. Note that the display device 510 can be anydevice, provided that it has a function for displaying an image on thedisplay surface. A cover may be provided to the display device 510 for apurpose of preventing damage or the like.

The display device 510 may be a LCD device, an OLED device, or a PDPdevice, for example.

Note that, in the optical device 500, the side of the first surface 562of the transparent substrate 560 is the side which is to be viewed.

In the optical device 500, the transparent substrate 560 has thefollowing optical characteristics:

the resolution index value T≤0.2,

the reflection image diffusiveness index value R≥0.2, and

the sparkle index value S≤60.

Note that the resolution index value T, the reflection imagediffusiveness index value R, and the sparkle index value S are valuesthat are obtained by the above-described methods, respectively.

Especially, the resolution index value T may preferably be less than orequal to 0.3 so as not to adversely affect visibility of a display body.In particular, the resolution index value T may preferably be less thanor equal to 0.2 with which it is difficult to perceive a difference invisibility. The reflection image diffusiveness index value R maypreferably be greater than or equal to 0.2 with which an outline of areflection image that tends to be viewed is blurred and the visibilityof the display body is enhanced. The sparkle index value may preferablybe less than or equal to 60 with which almost no sparkle can be sensed.

The transparent substrate 560 that has such optical characteristics hasa favorable resolution and a favorable anti-glare property. Thus, light(an image) from a side of the display device 510 can be relativelyclearly viewed.

Therefore, the optical device 500 that includes the transparentsubstrate 560 having such optical characteristics is suitable as anoptical device that is to be installed inside a vehicle, such as a carnavigation system.

Working Examples

Next, there are explained results of evaluation of resolution,evaluation of reflection image diffusiveness, and evaluation of sparklethat were implemented by using an actual transparent substrate.

(Regarding the Evaluation of the Resolution)

Various types of transparent substrates were prepared, and thesetransparent substrates were evaluated by the following method.

First, transparent substrates were prepared whose first surfaces wereanti-glare processed by corresponding various methods. Each of thetransparent substrates was formed of glass. The thickness of thetransparent substrates was selected in a range from 0.5 mm to 3.0 mm.

Further, a standard test chart that was formed of plastic (a highdefinition resolution chart I-type: produced by Dai Nippon Printing Co.,Ltd.) was prepared.

Next, each transparent substrate was disposed above the standard testchart. At that time, each of the transparent substrates was arranged, sothat a side of the first surface (i.e., the anti-glare processedsurface) of the transparent substrate was at the opposite side of thestandard test chart. Note that the space between each of the transparentsubstrates and the standard test chart was set to 1 cm.

Next, the standard test chart was visually observed through thetransparent substrate, and the limit of the bars that could be viewed(the number of TV lines) was evaluated. In this manner, a resolutionlevel by visual observation was evaluated for each of the transparentsubstrates. Note that the maximum value of the TV lines of this standardtest chart was 2000.

Next, by executing the operations such as shown in the above-describedstep S110 to step S130 by using a goniophotometer (GC5000L: produced byNIPPON DENSHOKU INDUSTRIES CO., LTD), the resolution index value T foreach of the transparent substrates was calculated from the expression(1). Note that, at step S120, the range of the reception angle of themeasurement device was from −85° to +85°, due to the constraints on theconfiguration as a measurement device. Since the transmitted lightvalues from −90° to −85° and from +85° to +90° were almost zero, thismeasurement range did not cause any significant impact for calculatingthe resolution index value T.

FIG. 11 shows an example of a relationship between a result ofdetermination of a resolution level by visual observation (the verticalaxis) and a resolution index value T (the horizontal axis) that wasobtained for each of the transparent substrates.

From FIG. 11, it can be seen that there is a negative correlationbetween them. Note that, in the vicinity of the resolution index value Tof 0.1, there were several transparent substrates for which theresolution levels by the visual observation were saturated at themaximum value of 2000.

This result indicates that the resolution index value T corresponds to atendency of the determination, by the observer, of the resolution by thevisual observation, and therefore suggests that the resolution of thetransparent substrate can be determined by using the resolution indexvalue T. In other words, it can be said that, by using the resolutionindex value T, the resolution of the transparent substrate can beobjectively and quantitatively determined.

(Regarding the Evaluation of the Reflection Image Diffusiveness)

Next, by using the above-described various transparent substrates thatwere used for the evaluation of the resolution, the reflection imagediffusiveness of each of the transparent substrates was evaluated by thefollowing method.

First, each of the transparent substrates was visually observed from theside of the first surface (i.e., the anti-glare processed surface), andthe reflection image diffusiveness was evaluated in twelve levels thatwere from level 1 to level 12. Note that the direction of theobservation was the direction of 45° with respect to the thicknessdirection of the transparent substrate.

FIG. 12 collectively shows, for reference, examples of the reflectionimage diffusiveness that correspond to level 1 to level 12,respectively. Note that this figure is obtained by separately takingphotographs of the transparent substrates that correspond to theselevels, respectively.

From FIG. 12, it can be seen that, along with level 1 to level 12, thereflection image on the transparent substrate gradually becomesinsignificant, namely, the reflection image diffusiveness of thetransparent substrate tends to be enhanced. Note that the state of level1 was obtained in the transparent substrate such that no anti-glareprocess was applied to each of its surfaces.

Next, by executing the operations such as shown in the above-describedstep S210 to step S230 by using a goniophotometer (GC5000L: produced byNIPPON DENSHOKU INDUSTRIES CO., LTD), the reflection image diffusivenessindex value R for each of the transparent substrates was calculated fromthe expression (2). Note that, at step S220, a range of the receptionangle of the measurement device was from +5° to +85°, due to theconstraints on the configuration as a measurement device. Since thereflected light values from 0° to +50 and from +85° to +90° were almostzero, the measurement range did not cause any significant impact forcalculating the reflection image diffusiveness index value R.

FIG. 13 shows an example of a relationship between a level of thereflection image diffusiveness that was evaluated by visual observation(the vertical axis) and the reflection image diffusiveness index value R(the horizontal axis) that was obtained for each of the transparentsubstrates.

From FIG. 13, it can be seen that there is a positive correlationbetween them.

This result indicates that the reflection image diffusiveness indexvalue R corresponds to a tendency of the level of the reflection imagediffusiveness by the visual observation by the observer, and thereforesuggests that the reflection image diffusiveness of the transparentsubstrate can be determined by using the reflection image diffusivenessindex value R. In other words, it can be said that, by using thereflection image diffusiveness index value R, the reflection imagediffusiveness of the transparent substrate can be objectively andquantitatively determined.

(Regarding the Evaluation of the Sparkle)

Next, by using the above-described various transparent substrates thatwere used for the evaluation of the resolution, the sparkle of each ofthe transparent substrates was evaluated by the following method.

First, each of the transparent substrates was directly disposed on aside of a display surface of a display device (iPhone 4S (registeredtrademark)). At that time, each of the transparent substrates wasdisposed on the side of the display surface of the display device, sothat the first surface of each of the transparent substrates (i.e., theanti-glare processed surface) was at the side of the observer. Note thatan image that was displayed on the display device was a single-colorgreen image, and the size of the image was set to 7.5 cm×5.1 cm.

Next, in this state, each of the transparent substrates was visuallyobserved from the side of the first surface, and the sparkle wasevaluated in 11 levels that were from level 0 to level 10. Level 0indicates that almost no sparkle can be observed, and level 10 indicatesthat the sparkle is extremely significant. Further, the values of thelevels between them have tendency such that, as the value becomegreater, the sparkle becomes more significant.

FIG. 14 shows, for reference, examples of the transparent substratesthat indicate the sparkle of level 0 and the sparkle of level 7,respectively. Note that the level 0 was obtained for an optical devicethat included a transparent substrate and a display device. The surfacesof the transparent substrate were not anti-glare processed.

Next, by executing the operations such as shown in the above-describedstep S320 to step S330, an ISC-A value of each of the transparentsubstrates was obtained by using the software Eyescale-4W (produced byI-System Co., Ltd.), and the sparkle index value S was set to thatvalue.

FIG. 15 shows an example of a relationship between the sparkle indexvalue S (the vertical axis) and the level of the sparkle by the visualobservation (the horizontal axis).

From FIG. 15, it can be seen that there is a positive correlationbetween them.

This result indicates that the sparkle index value S corresponds aresult of the determination of the sparkle through the visualobservation by the observer, and therefore suggests that the sparkle ofthe transparent substrate can be evaluated by using the sparkle indexvalue S. In other words, it can be said that, by using the sparkle indexvalue S, the sparkle of the transparent substrate can be objectively andquantitatively determined.

In this manner, it has been verified that the resolution index value T,the reflection image diffusiveness index value R, and the sparkle indexvalue S can be used as quantitative indexes of the resolution, thereflection image diffusiveness, and the anti-glare property of thetransparent substrate, respectively.

The present invention can be utilized, for example, for an opticaldevice in which a transparent substrate is disposed on a side of adisplay surface of a display device, such as a LCD device, an OLEDdevice, and a PDP device.

What is claimed is:
 1. A glass plate for a display surface of a displaydevice, wherein the glass plate that is disposed on a side of a displaysurface of a display device, the glass plate has a first surface havingan anti-glare property and a second surface that faces the firstsurface, the glass plate satisfies a resolution index value T≤0.2, areflection image diffusiveness index value R≥0.2, and a sparkle indexvalue S≤60, the resolution index value T is calculated by expression,the resolution index value T=(brightness of all transmittedbeams−brightness of 0° transmitted light beam)/(brightness of alltransmitted light beams), where a first light beam is irradiated from aside of the second surface of the glass plate in a direction of an angleof 0° which is a direction that is parallel to a thickness direction ofthe glass plate, and the brightness of the 0° transmitted light beamwhich is a transmitted light beam that is transmitted from the firstsurface is measured, a light reception angle of receiving a first lightbeam with respect to the first surface of the glass plate is varied in arange from −90° to +90°, and the brightness of all transmitted beamsthat are transmitted from a side of the first surface is measured, thereflection image diffusiveness index value R is calculated byexpression, the reflection image diffusiveness index value R=(brightnessof all reflected beams−brightness of a 45° regular reflectedbeam)/(brightness of all reflected beams), where a second light beam isirradiated from the side of the first surface of the glass plate in adirection of 45° with respect to the thickness of the glass plate, thebrightness of the 45° regular reflected light beam which a light beamthat is specularly reflected by the first surface is measured, a lightreception angle of receiving the reflected beam that is reflected by thefirst surface is varied in a range from 0° to +90°, and the brightnessof all reflected beams that are reflected by the first surface ismeasured, and the sparkle index value S is obtained by setting a valueoutput by an analysis software as the sparkle index value S, where theglass plate is positioned at the side of the display surface of thedisplay device such that the second surface is at the side of thedisplay device, a photograph of the glass plate is taken from the sideof the first surface to obtain an image, and the image is analyzed bythe analysis software.
 2. The glass plate according to claim 1, whereinthe first surface having the anti-glare property is obtained byprocessing a surface of the glass plate.
 3. The glass plate according toclaim 2, wherein the first surface having the anti-glare property isobtained by applying a frost process to the surface of the glass plate.4. The glass plate according to claim 2, wherein the first surfacehaving the anti-glare property is obtained by applying an etchingprocess to the surface of the glass plate.
 5. The glass plate accordingto claim 2, wherein the first surface having the anti-glare property isobtained by applying a sandblast process to the surface of the glassplate.
 6. The glass plate according to claim 2, wherein the firstsurface having the anti-glare property is obtained by applying a lappingprocess to the surface of the glass plate.
 7. The glass plate accordingto claim 1, wherein the first surface having the anti-glare property isobtained by coating a surface of the glass plate with a film having theanti-glare property.
 8. The glass plate according to claim 7, whereinthe film having the anti-glare property is a film including silica. 9.The glass plate according to claim 1, wherein the display device is oneof a LCD device, an OLED device, and a PDP device.
 10. The glass plateaccording to claim 1, wherein the glass plate is formed of soda-limeglass or aluminosilicate glass.
 11. The glass plate according to claim10, wherein the glass plate is treated by a chemically strengtheningprocess applied to at least one of the first surface and the secondsurface of the glass plate.
 12. The glass plate according to claim 10,wherein the first surface having the anti-glare property is obtained byapplying a frost process to a surface of the glass plate.
 13. The glassplate according to claim 10, wherein the first surface having theanti-glare property is obtained by applying an etching process to asurface of the glass plate.
 14. The glass plate according to claim 10,wherein the first surface having the anti-glare property is obtained byapplying a sandblast process to a surface of the glass plate.
 15. Theglass plate according to claim 10, wherein the first surface having theanti-glare property is obtained by applying a lapping process to asurface of the glass plate.
 16. The glass plate according to claim 10,wherein the first surface having the anti-glare property is obtained bycoating a surface of the glass plate with a film having the anti-glareproperty.
 17. The glass plate according to claim 16, wherein the filmhaving the anti-glare property is a film including silica.
 18. The glassplate according to claim 1, wherein the glass plate is configured to beapplied to an optical device that is to be installed inside a vehicle.19. The glass plate according to claim 1, wherein the glass plate isformed of soda-lime glass.
 20. The glass plate according to claim 1,wherein the glass plate is formed of aluminosilicate glass.